A Self‐Assembled Single‐Ion Membrane via In Situ Neutralization Enables Triple Stability in Ultrahigh‐Nickel Cathodes

Ultrahigh-nickel layered oxides (Ni ≥ 90%) offer exceptional specific capacity but suffer from severe air sensitivity, poor thermal stability, and rapid capacity decay. To date, it is still a significant challenge to address all three bottlenecks simultaneously with a single and integrated strategy, which have severely hindered the large-scale commercial deployment of ultrahigh-nickel layered oxide cathodes. Herein, a novel self-assembling single-ion conductor membrane, featuring exceptional hydrophobicity, outstanding thermal stability (>445°C), and strong Donnan exclusion against PF₆ ^- anions, is rationally engineered to holistically enhance the air stability, heat resistance, and electrochemical performance of ultrahigh-nickel layered oxide cathodes. The N-cyano-sulfonamide group on membrane undergoes an in-situ neutralization reaction with residual LiOH/Li₂CO₃ on the LiNi_0.9Co_0.05Mn_0.05O₂ (NCM9055), which drives it migration toward the cathode surface and form a self-assembled protective coating with pronounced hydrophobicity and strong Donnan exclusion. As a result, 3.5 Ah NCM9055/Gr pouch battery demonstrates a commendable capacity retention of 94.97% after 500 cycles. meanwhile the onset temperature of thermal runaway was significantly elevated from 124.2°C to 158.2°C. This work establishes a unified interfacial engineering paradigm that simultaneously addresses the long-standing triad of bottlenecks plaguing ultrahigh-nickel layered oxide cathodes, offering a scalable and industrially viable pathway toward safe, long-life, high-energy-density lithium-ion batteries (LIBs).